Active implantable medical devices (AIMDs) are commonly used to apply electrical pulses to various parts of the human body, such as the heart of a patient with a cardiovascular condition. As further examples, AIMDs may comprise cardiac pacemakers and defibrillators, spinal cord stimulators (SCS) for pain therapy, dorsal root ganglion stimulators (DRG stimulators), motor cortex stimulators, diaphragm stimulators, cochlear implants, and deep brain stimulators (DBS) for epilepsy therapy. Other examples of AIMDs include gastric nerve stimulators, bladder stimulators, and stimulators for peripheral or cranial nerves [e.g., for the treatment of migraine respectively sleep apnea (hypoglossal) and epilepsy (vagal)]. AIMDs can even be used to administer drugs, to monitor vitals, to minimize the effects of movement disorders, or to monitor or minimize psychiatric conditions. Those having ordinary skill in the art will appreciate that the above list of devices and applications for AIMDs is not in any way exhaustive. Indeed, new applications for AIMDs are constantly reported and evolving.
A typical AIMD includes an active part, such as a metal can containing electrical circuits that generate therapeutic electric pulses; a power supply, such as a primary cell or a rechargeable battery; and a one- or two-way radio that allows the AIMD to communicate with components that are not implanted, such as a programming device, for example. Many AIMDs also include a conducting component, a lead, and an extension. The active part is usually coupled to the lead, which along with the extension delivers the therapeutic pulses to a recipient body part such as a heart, a brain, a spinal cord, or nerves. It is common for the active part to be implanted at sites that are relatively comfortable for the patient. For instance, active parts are typically implanted in a pectoral (i.e., the chest), an infracostal, or a gluteal area. The lead may be connected either directly to the active part or, in some cases where longer distances have to be bridged, by way of an extension that is used to connect the lead and the active part. The total length of a lead an extension can in many cases exceed 100 cm. Such a length does not affect the quality of the stimulation and do not overcomplicate the surgical procedure, as these components are well tolerated by the subcutaneous tissue where these components are positioned using special tunneling devices. Extensions that are too short can cause unwanted mechanical stress, which in some cases can result in wire fractures. For this reason, surgeons prefer a slight surplus in terms of length, as the surgeons can kink and/or coil the excess lead or extension. Moreover, tunneling is a routine procedure that is simple and safe. However, those having ordinary skill in the art will understand that tunneling can be a delicate task when performed in certain locations, such as the neck, where crossing vessels can lead to hematomas.
However, one of the major problems of using a lengthy conducting material that passes through subcutaneous tissue (i.e., the AIMD lead and its extensions) is that the lengthy conducting material acts as an antenna. As a result, the lengthy conducting material can become problematic when a patient is exposed to an electromagnetic field that interacts with the lengthy conducting material. Many patients having AIMDs must avoid strong electromagnetic fields created by common devices such as metal detectors, article surveillance security systems, airport scanners, cell phones, and wireless communication devices, to name a few. Electromagnetic fields are also used in one the most important medical imaging technologies, namely, Magnetic Resonance Imaging (MRI). Thus, patients with AIMDs are typically not allowed to access MRI scanners, which are very important diagnostic tools.
Therefore, a need exists for a device that prevents, or at least substantially reduces, the effects of electromagnetic fields on AIMDs.